The fabrication of integrated circuits involves the creation of several layers of materials that interact in some fashion. One or more of these layers may be patterned so various regions of the layer have different electrical characteristics, which may be interconnected within the layer or to other layers to create electrical components and circuits. These regions may be created by selectively introducing or removing various materials. The patterns that define such regions are often created by lithographic processes. For example, a layer of photoresist material is applied onto a layer overlying a wafer substrate. A photomask (containing clear and opaque areas) is used to selectively expose this photoresist material by a form of radiation, such as ultraviolet light, electrons, or x-rays. Either the photoresist material exposed to the radiation, or that not exposed to the radiation, is removed by the application of a developer. An etch may then be applied to the layer not protected by the remaining resist, and when the resist is removed, the layer overlying the substrate is patterned.
Lithographic processes such as that described above are typically used to transfer patterns from a photomask to a device. As feature sizes on semiconductor devices decrease into the submicron range, there is a need for new lithographic processes, or techniques, to pattern high-density semiconductor devices. Several new lithographic techniques which accomplish this need and have a basis in imprinting and stamping have been proposed. One in particular, Step and Flash Imprint Lithography (SFIL), has been shown to be capable of patterning lines as small as 20 nm.
Overall, SFIL techniques benefit from their unique use of photochemistry, ambient temperature processing, and the low contact pressure required to carry out the SFIL process. During a typical SFIL process, a substrate is coated with an organic planarization layer, and brought into close proximity of a transparent SFIL template, typically comprised of quartz, containing a relief structure and coated with a low surface energy material. A photocurable organic solution is deposited between the template and the coated substrate. Using minimal pressure, the template is brought into contact with the substrate, and more particularly the photocurable organic layer. Next, the organic layer is cured, or exposed, at room temperature by photoillumination through the template. The light source typically uses ultraviolet radiation, deep ultraviolet, or broad band radiation. A range of wavelengths (150 nm-500 nm) is possible, depending upon the transmissive properties of the template and photosensitivity of the photocurable organic. The template is next separated from the substrate and the organic layer, leaving behind an organic replica of the template relief on the planarization layer. This pattern is then etched with a short halogen break-through, followed by an oxygen reactive ion etch (RIE) through the planarization layer to form a high-resolution, high aspect-ratio feature in the organic layer and planarization layer.
The distinction between a lithographic mask and a lithographic template should be noted. A lithographic mask is used as a stencil to impart an aerial image of light into a photoresist material. A lithographic template has a relief structure formed into its surface, creating a form or mold. During SFIL, a pattern is defined when a photocurable liquid flows into the relief structure and is subsequently cured. During standard imprint lithography, a pattern is defined when a material present on the surface of a substrate material plastically deforms in response to pressure exerted thereupon by a patterned template. The attributes necessary for masks and templates, therefore are quite different.
One process of fabricating SFIL templates includes applying a layer of chrome, 15-100 nm thick, onto a transparent quartz plate. A resist layer is applied to the chrome and patterned using either an electron beam or optical exposure system. The resist is then placed in a developer to form patterns on the chrome layer. The resist is used as a mask to etch the chrome layer. The chrome then serves as a hard mask for the etching of the quartz plate. Finally, the chrome is removed, thereby forming a quartz template containing relief structures in the quartz.
SFIL technology has been demonstrated to resolve features as small as 20 nm. As such, a wide variety of feature sizes may be drawn on a single wafer. Certain problems exist though with this SFIL template fabrication methodology. In particular, problems exist with the conventional resist, masking, and etch process, and defects formed on the relief surface of the template. More specifically, problems exist with respect to the number of required steps needed to fabricate the template, namely, the etching of the chrome, the etching of the quartz material, and the required etch and resist removal steps and defects that are present in the template relief surface subsequent to the etch process. It should be understood that each etching step increases the probability of defects and changes in feature dimension. These defects can be negative in nature, meaning there is an absence of relief material on the template relief surface, and are referred to herein as gap defects in that they define a “gap” in the relief material. Alternatively, these defects can be positive in nature, meaning there is extraneous relief material present on the template surface that does not define a desired portion of the relief structure. Defect repair, irrespective of negative or positive, is a critical requirement which must be addressed in SFIL.
In addition, there exist problems with respect to electron-beam writing of the template and the inspection of the template subsequent to fabrication. In particular, a charge dissipation layer must be present, in order to avoid charge build-up during electron-beam exposure. Inspectability is not readily achievable due to the template being comprised of a single homogeneous material. Typical inspection systems use either light (ultraviolet or deep ultraviolet) or electrons to determine feature size and detect unwanted defects on the template. Light-based systems require a difference in reflection or index of refraction between patterned and unpatterned areas of the template to provide good image contrast. Likewise, an electron-based system requires a difference in atomic number between patterned and unpatterned areas of the template. To overcome this problem, a template comprised of multiple materials having either different optical properties, electron scattering properties, or different atomic numbers would allow for inspection, a necessity for sub-100 nm features.
Accordingly, there is a need to simplify the fabrication process of forming SFIL templates. Specifically, it would be beneficial to provide for a template in which fewer processing steps are required to fabricate a template for use in SFIL technology, a means for repairing defects formed within the relief structure of the SFIL template, and a template in which inspection for sub-micron structures is achievable.
It is a purpose of the present invention to provide for an improved lithographic template including a repaired defect, a method of fabricating the improved lithographic template, a method for repairing defects present in the template, and a method for making semiconductor devices with the improved lithographic template in which minimal fabrication steps are utilized including a means for repairing defects formed within the relief structure of the SFIL template.
It is another purpose of the present invention to provide for an improved lithographic template including a repaired defect, a method of fabricating the improved lithographic template, a method for repairing defects present in the template, and a method for making semiconductor device with the improved lithographic template in which repair of defects formed on the template relief surface is obtainable.
It is still another purpose of the present invention to provide for an improved lithographic template, a method of fabricating the improved lithographic template, and a method for making semiconductor devices with the improved lithographic template in which improvement in the template and fabrication process provides for higher throughput and cost effectiveness.